Fermentation of fruit juices

ABSTRACT

A method of introducing yeast into a fruit juice such as grape must to be fermented is disclosed. The method comprises feeding dry yeast into a flowing stream of the fruit juice and delivering the flowing stream of fruit juice with the yeast in it to a mixer (10). The fruit juice and yeast emerging from the mixer is fed into a fermentation tank. The yeast can include nutrients selected from inactivated yeasts, yeast autolysates, yeast cell hulls, yeast extracts, amino acids, peptides, proteins, sterols, ergosterol, thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine, minerals and inorganic nitrogen in the form of ammonium salts.

FIELD OF THE INVENTION

THIS INVENTION relates to the fermentation of fruit juices to producealcoholic beverages.

BACKGROUND TO THE INVENTION

Modern fermentation processes used for the production of wine, cider,beer, sake, potable ethanol and other fermentation products include theuse of selected yeasts. Selected yeasts are made commercially availableto the producer in dry forms, either as vermicellae (Instant Dry YeastIDY) or pellets (Active Dry Yeast ADY). These dry forms are standard inthe yeast industry as they allow long term storage while keeping a veryhigh viability in the range 1 to 3×10¹⁰ colony forming units per gram ofdry products. Commercial dry yeasts include more than 500 differentstrains. Most of them belong to Saccharomyces genus and a few to othergeni such as Torulaspora, Metschnikowia, Pichia or Candida.

The use of a selected yeast strain is an essential quality step inmodern winemaking and other fermentation industries. For winemaking,grapes are crushed or pressed to release a grape must. As harvestedgrapes are not pasteurised and sterilized, they contain a vastpopulation of indigenous (or wild) yeasts of different genii. Yeastcells of the selected commercial strain compete with this indigenousflora. It is therefore essential for the winemaker to ensure a“successful implantation” of the selected yeast strain. This means thatthe commercial yeast must be added with adequate viability so that itbecomes predominant among naturally occurring yeasts in the fermentationmedia. It is accepted in the fermentation industry, and especially inthe winemaking industry, that such yeasts must be added after a carefulrehydration step. The objective of rehydration is to achieve the maximumviability (expressed as the percentage of live cells) immediately priorto introduction of the rehydrated yeast into the grape must. Rehydrationis dealt with extensively in the article entitled “Rehydration Protocolsfor Active Dry Wine Yeasts and the Search for Early Indicators of YeastActivity” published in Am. J. Enol. Vitic. 57:4 (2006). Applicant is notaware of any disclosure of any procedure which does not include therehydration step with all its inherent difficulties that are known towinemakers worldwide.

Standard rehydration includes the following steps:

-   -   Preparation of a water solution at 37 to 40 ° C. in a        rehydration receptacle (a bucket or a small tank). Sugar or        grape must is added to reach 40 g/l of sugar;    -   Addition of ADY or IDY to this warm solution with continuous        stirring;    -   mixing (gentle to vigorous);    -   the solution stands for 20 min to achieve rehydration. Formation        of foam due to the production of CO2 is visible at this stage;    -   preferably the solution is diluted progressively using grape        must from the tank to be fermented. This is to avoid a        temperature shock if there is a large difference with respect to        the cold must;    -   addition to fermentation tank (the temperature of the must is        generally in the range 10-25 ° C. at this stage).

This standard rehydration process is common industry practice. Howeverit has a number of drawbacks:

-   -   It is tedious and time consuming in a busy period for        winemakers;    -   Following all steps is complex and often not followed in        practice;    -   The procedure is not convenient for large quantities of yeast        (above 50 kg);    -   The rehydration vessels have to be cleaned thoroughly between        successive rehydration processes to avoid cross-contamination        between fermentation tanks when different yeast strains are        used;    -   Considerable time is needed to complete the procedure;    -   Water is consumed;    -   When the procedure is not followed properly, the viability of        the yeast is low and successful of implantation of the selected        strain cannot be guaranteed.

One object of the present invention is to provide a method of, andapparatus for, delivering dry yeast (ADY or IDY) to a fermentation tank.A further object is to provide a yeast formulation incorporatingadditives for delivery to a fermentation tank.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided amethod of introducing yeast into a fruit juice to be fermented whichmethod comprises feeding dry yeast into a flowing stream of the fruitjuice, delivering the flowing stream of fruit juice with the yeast in itto a mixer, and feeding the fruit juice and yeast emerging from themixer into a fermentation tank.

The term “yeast” when used herein means a yeast strain of the geniiSaccharomyces, Torulaspora, Metschnikowia, Pichia or Candida, or amixture thereof.

The term “viable yeast” when used herein means a yeast able to reproduceunder favorable conditions while actively fermenting.

The term “inactivated yeast” when used herein means a yeast which hasbeen disrupted and is no longer able to reproduce.

The mixer is preferably a high shear mixer.

The yeast can be in powder, vermicelli or pellet form.

The preferred form of the method comprises the steps of feeding theyeast from a hopper along a first pipe leading to a pipe junction,feeding fruit juice along a second pipe leading to said pipe junction,and feeding the mixed yeast and fruit juice along a pipe which leadsaway from said junction to the inlet of the high shear mixer.

The method can further comprise dispersing dry yeast nutrients in thedry viable yeast to form a dry mixture of nutrients and yeast, andintroducing the dry mixture into the fruit juice. Such nutrients can beselected from inactivated yeasts, yeast autolysates, yeast cell hulls,yeast extracts, amino acids, peptides, proteins, sterols , ergosterol,thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine,minerals and inorganic nitrogen as ammonium salts and each can be usedalone or in combination with other nutrients.

The combined introduction of these nutrients improves yeast viabilityafter introduction into fruit juice and reduces the lag phase (initialphase before fermentation activity is noticeable). Therefore, itimproves the implantation of the selected yeast into the fruit juice andensures the requisite fermentation.

The method can include the preliminary steps of mixing yeast and thenutrients into the form of a cream before drying. Preferably the creamis filtered and the filter cake is extruded to form vermicelli orpellets before the drying step

According to a further aspect of the present invention there is providedan installation which comprises a mixer having an inlet, a pipe leadingfrom a pipe junction to said inlet, first and second pipes leading tosaid pipe junction and connected one to a source of dry yeast and theother to a source of fruit juice, a fermentation tank and a feed pipeleading from the outlet of said mixer to said fermentation tank.

The mixer is preferably a high shear mixer.

According to a still further aspect of the present invention there isprovided a formulation which comprises dry viable yeasts mixed with oneor more dry nutrients selected from inactivated yeasts, yeastautolysates, yeast hulls, yeast extracts, amino acids, peptides,proteins, sterols , ergosterol, thiamin, biotin, pantothenic acid,niacin, riboflavin, pyridoxine, minerals and inorganic nitrogen in theform of ammonium salts.

The nutrients can represent 10 to 70% by weight of the formulation.

The dry viable yeast can be mixed with inactivated yeast.

The dry viable yeast can constitute at least 20% of the dry weight ofthe yeast formulation. Preferably the dry viable yeast constitutes morethan 30%, preferably more than 40%, preferably more than 50%, preferablymore than 60% of the dry weight of the yeast formulation.

The yeast formulation is preferably produced by mixing the viable yeastand the nutrients in the form of a cream, filtering the cream andthereafter extruding and drying the filter cake.

The present invention also provides a method of producing wine whichcomprises feeding dry yeast into a flowing stream of grape must,delivering the flowing stream of grape must with the yeast dispersed init to a mixer, feeding the grape must and yeast emerging from the mixerinto a fermentation tank, and thereafter permitting fermentation toproceed in the fermentation tank.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the present invention, and to show how thesame may be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings in which;

FIG. 1 diagrammatically illustrates an installation in accordance withthe present invention, and

FIG. 2 illustrates the influence of the present invention on theperformance of yeast in fermentation.

DETAILED DESCRIPTION OF THE DRAWING

The installation 10 illustrated in FIG. 1 comprises a high shear mixer12. A pipe 14 leads from a pipe junction 16 to the inlet 18 of the mixer12. A feed pipe 22 leads downwards from a hopper 24 and thenhorizontally to the pipe junction 16. A shut-off valve 26 is provided atthe outlet of the hopper. The hopper can contain yeast pellets, yeastpowder or yeast in the form of vermicellae. A mixture of yeasts can beprovided and there can also be nutrients as will be describedhereinafter.

A further pipe 28 leads from a source of fruit juice to the pipejunction 16. The fruit juice can be grape must if wine is to be made orapple or pear juice if cider is being made. A pipe 30 leads from theoutlet of the high shear mixer 12 to a fermentation tank (not shown).

A suitable high shear mixer is that available from Silverson under thename “Flashmix”. A Flashmix mixer comprises a cylindrical stator 32within which there is a high speed rotor 34. The stator is within anouter casing 36. The rotor is configured to create a suction effect atthe inlet 18. When the valve 26 is opened the suction effect draws yeastfrom the hopper 24 into the chamber bounded by the stator and in whichthe rotor turns. Centrifugal force drives the yeast and fruit juiceoutwardly towards the stator and milling takes place in the narrow gapbetween the stator and the rotor. The stator has perforations in it andthe yeast is subjected to high hydraulic shear as it passes throughthese perforations to the outlet of the Flashmix. The motor which drivesthe rotor is not shown in the drawing.

For winemakers and the wine industry, the direct addition of yeast intogrape must, that is the addition of yeast without a previous rehydrationstep, using the powder/liquid high shear mixer described above, brings alarge number of substantial benefits when compared to the establishedindustry practice (the rehydration process using hot water). Thesebenefits include:

-   -   Time savings; the addition is almost instantaneous and does not        require any follow up;    -   Labour savings: a standard rehydration process may take 2-4        hours in large wineries;    -   Efficiency: the success of the yeast implantation does not        depend on worker skills or attention;    -   Simplicity: there is no need to have access to hot water;    -   Flexibility: the same equipment can be used for any type of dry        yeast quantities, from a few hundred grams to hundreds of        kilograms;    -   The method avoids cross-contamination between strains as the        hopper and the rotor/stator mixer are designed for easy        cleaning;    -   Water savings: no water is used for rehydration and for cleaning        the bucket or other receptacle;    -   Energy savings: energy consumption is smaller than when using        hot water;    -   Professionalism: the image of the winery is improved by the use        of a modern equipment.

The present invention will now be explained in more detail withreference to the following winemaking examples. For comparison purposes,in all examples, the method of the present invention and a standardrehydration process were used.

EXAMPLES Example 1

the test was carried out using active dry yeasts in vermicellae (strainFermicru XL) and pellet (strain Anchor Vin13) forms.

The grape must used had the following characteristics:

Cultivar: Grenache blanc

Sugar: 230 g/L

pH: 3,37

Nitrogen (Free Available Nitrogen): 195 mg/L

Turbidity: 94 NTU

Free SO₂: 10 mg/L

Total SO₂: 45 mg/L

Pasteurized must with 1.7 10E3 wild microorganisms/ml

Temperature: 14 ° C.

Dry yeast was added at a dosage of 200 mg/l directly into the grape mustaccording to the present invention. Specifically dry yeasts are placedin the hopper 24 and grape must is supplied through the pipe 28.

Dry yeast was added at a dosage of 200 mg/l after the following standardrehydration procedure: heating a solution of glucose at 50 g/l up to 37°C. ; addition of dry yeast to this warm solution with continuousstirring; mixing; allowing to stand for 20 min; three successivedilutions with one volume of cold grape must; addition of the rehydratedyeast suspension into the fermentation tank containing the cold grapemust.

After addition of yeast according to those two procedures, thefermentation tanks were held at 18 to 20° C. and the relevant parameterswere monitored to follow the yeast population and the conditions offermentation kinetics.

TABLE 1 Comparison of fermentation parameters and yeast viability duringethanol fermentation of a Grenache grape must inoculated with dry yeastadded directly according to the present invention, and according to thestandard rehydration procedure. Fermicru XL Anchor Vin 13 Direct Directaddition addition Mode of according according addition of to presentStandard to present Standard dry yeast invention rehydration inventionrehydration Lag phase (h) 30 24 35 29 Living Yeast 42.4 43 13.4 12.2 at45 h (10E6 cfu/ml) Residual 21.1 22.8 4.8 8.1 sugars (in g/l) at 550 h

There was no significant difference between the fermentation tank usedwith yeast added according to the present invention and the tank usedwith yeast added according to standard rehydration procedure. Thefigures set out in the tables are consequently not influenced byanything other than the mode of yeast addition.

Example 2

The test was carried out using active dry yeasts in vermicellae (strainFermicru LS2) and pellet (strain Anchor Vin13) forms.

The grape must used had the following characteristics:

Cultivar: Syrah

Direct pressing

Sugar: 183 g/L

pH: 3,66

Nitrogen (Free Available Nitrogen): 105 mg/L

Turbidity: 30 NTU

Free SO₂: 12 mg/L

Total SO₂: 33 mg/L

Non Pasteurized must with 1.8 10E5 wild microorganisms/ml

Temperature: 16-17° C.

Dry yeast was added, at a dose of 200 mg/l directly into the grape must,according to the present invention. Specifically dry yeasts are placedin the hopper 24 and grape must is supplied through the pipe 28.

A standard rehydration procedure as follows was used: heating a blend of25% grape must in water up to 37° C. ; addition of dry yeast to thiswarm solution with continuous stirring, mixing; allowing to stand for 20min; three successive dilutions with one volume of cold grape must;addition of the rehydrated yeast suspension into the fermentation tankcontaining the cold grape must.

After the addition of yeast at 200 mg/l according to those twoprocedures, the fermentation tanks were kept at 18° C. and relevantparameters were monitored to follow the yeast population and theconditions of fermentation kinetics.

TABLE 2 Comparison of fermentation parameters and yeast viability duringethanol fermentation of a Syrah grape must inoculated with dry yeastadded directly according to the present invention, or according tostandard rehydration procedure. Fermicru LS2 Anchor Vin 13 Direct Directaddition addition Mode of according according addition of to presentStandard to present Standard dry yeast invention rehydration inventionrehydration % of living 86 86 78 84 yeast 24 h after addition to grapemust Implantation 80 80 90 100 control: % of selected yeast strain amongtotal yeast population Time to 9 9 9 8 complete fermentation (days)Residual 0.44 0.17 0.02 0.02 sugars (g/l) at 240 h

There was no significant difference between the fermentation tank usedto add yeast according to the present invention and the tank used to addyeast according to the standard rehydration procedure. The figures setout above were consequently not influenced by anything other than themode of yeast addition.

The different Syrah wines obtained were analysed at the end offermentation.

TABLE 3 Composition of rosé wines obtained after complete ethanolfermentation of a Syrah must inoculated with dry yeast added directlyaccording to the present invention, and according to standardrehydration procedure. Fermicru LS2 Anchor Vin 13 Direct Direct additionaddition Mode of according according addition of to present Standard topresent Standard dry yeast invention rehydration invention rehydrationEthanol 11.65 11.6 11.6 11.55 content (%) Total acidity 3.9 4.05 3.753.85 (in g/l sulfuric acid) Volatile 0.11 0.15 <0.06 <0.06 acidity (ing/l acetic acid) Isoamyl 8.64 7.08 7.56 6.63 acetate (mg/l) hexylacetate 0.76 0.63 0.65 0.61 (mg/l) ethyl 1.79 1.53 1.51 1.44 hexanoate(mg/l) ethyl 1.31 1.07 1.40 1.28 octanoate (mg/l)

The completion of ethanol fermentation in all tanks was reflected insimilar ethanol content in all wines.

Surprisingly, the wines obtained using the winemaking process includingthe introduction of dry yeast in accordance with the present inventionhave been found to be of higher quality than control wines made from thesame grape must but after addition of rehydrated yeasts. This increasedquality was noticeable as the wines obtained had a higher ester content(more aroma) and a lower acetic acid content (lower volatile acidity).

Example 3

A test was carried out using two different active dry yeastspreparations of the same strain (commercial yeast Fermicru AR2) invermicellae forms.

-   -   Standard commercial yeast Fermicru AR2, produced according to        standard yeast manufacturing practices.    -   A Yeast Product AR2 produced as described below:    -   Strain AR2 is grown as fresh cream yeast, according to standard        yeast manufacturing practices    -   The cream yeast is blended with dry inactivated yeast in a ratio        of viable yeast/inactivated yeast 70/30 (dry weight basis)    -   The blend obtained is then vacuum filtered, extruded and dried        according to standard yeast manufacturing practice.    -   This Yeast Product AR2 contains 70% viable dry yeasts on a dry        weight basis

The characteristics of both yeasts used for Example 3 are listed inTable 4

TABLE 4 Characteristics of standard commercial Fermicru AR2 and YeastProduct AR2 commercial Fermicru Yeast Product AR2 AR2 Total viable yeastcount 4.00E+10 2.49E+10 (CFU/g) Active yeast >99 70 (% dry matter)Inactive yeast <1 30 (% dry matter) Dry matter % 94.00 92.24

The grape must used had the following characteristics:

Cultivar: Chardonnay

Sugar: 210 g/L

pH: 3.66

Nitrogen (Free Available Nitrogen): 177 mg/L

Turbidity: 40 NTU

Free SO₂: 5 mg/L

Total SO₂: 18 mg/L

Temperature: 19.5° C.

The standard commercial yeast Fermicru AR2 was added at a dosage of 200mg per liter of grape must directly into the grape must according to thepresent invention. Specifically dry yeasts are placed in the hopper 24and grape must is supplied through the pipe 28.

The Yeast product AR2 was added at a dosage of 300 mg per liter of grapemust directly into the grape must according to the present invention.Specifically dry yeasts are placed in the hopper 24 and grape must issupplied through the pipe 28. As this yeast product contains 70% ofviable yeasts, the total population added per litre of must was similarto Fermicru AR2.

After direct addition of both yeasts to the Chardonnay must according tothe method of present invention, both fermentation tanks were held at18° C. and the relevant parameters were monitored during the initial 80hours of fermentation, to follow the yeast population and the conditionsof fermentation kinetics. The fermentation kinetic curves, expressed asthe instant production of CO2 (dCO2/dt, expressed in g/l/h) as afunction of time, clearly show (FIG. 2) a better start of thefermentation with the Yeast Product AR2 than with the commercial yeastFermicru AR2.

In FIG. 2 the line designated 1 shows the rate of carbon dioxide releasewith time when the commercial yeast Fermicru AR2 is fed into the grapemust in accordance with the method of the present invention. Line 2shows the rate of carbon dioxide production with time when the YeastProduct AR2 is fed into the grape must in accordance with the method ofthe present invention.

This faster start of fermentation is also reflected in otherfermentation and yeast viability parameters, as shown in Table 5. Thetotal yeast population per ml of fermenting must was very significantlylarger when the Yeast Product AR2 was used than the commercial yeastFermicru AR2.

TABLE 5 Comparison of fermentation parameters and yeast viability duringethanol fermentation of a Chardonnay grape must inoculated with acommercial yeast (Fermicru AR2) or with an experimental Yeast product(AR2) added directly to the must according to the present invention.Commercial yeast Fermicru Yeast Product AR2 AR2 Lag phase (hours) 28 24% of living yeast 24 h after direct 57 63 addition to grape must Totalyeast population at 18 9.2 14 hours (in CFU/ml) Total yeast populationat 50 42 56 hours (in CFU/ml) Total yeast population at 74 65.2 74 hours(in CFU/ml) Residual sugars (g/l) at 80 h 61.4 55.1

1. A method of introducing yeast into a fruit juice to be fermented, themethod comprising: dispersing dry yeast nutrients in a dry viable yeastto form a dry mixture of nutrients and viable yeast; feeding the drymixture of nutrients and viable yeast into an uninterrupted flowingstream of fruit juice such that the dry yeast comes into direct contactwith the fruit juice without a previous rehydration step of the dryyeast; delivering the flowing stream of fruit juice with the yeast in itto a mixer; and feeding the fruit juice and yeast emerging from themixer into a fermentation tank.
 2. The method as claimed in claim 1,wherein the mixer is a high shear mixer.
 3. The method as claimed inclaim 1, wherein the yeast is in powder, vermicelli or pellet form. 4.The method as claimed in claim 1, further comprising: feeding the drymixture of nutrients and yeast from a hopper along a first pipe leadingto a pipe junction; feeding the fruit juice along a second pipe leadingto the pipe junction; and feeding the mixed yeast and fruit juice alonga pipe which leads away from said junction to an inlet of the mixer. 5.The method as claimed in claim 1, wherein said dry yeast nutrients areselected from inactivated yeasts, yeast autolysates, yeast cell hulls,yeast extracts, amino acids, peptides, proteins, sterols, ergosterol,thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine,minerals and inorganic nitrogen in the form of ammonium salts.
 6. Themethod as claimed in claim 1, further comprising: mixing the dry viableyeast and the dry yeast nutrients into a form of a cream; filtering thecream; and drying a filter cake.
 7. The method as claimed in claim 6,wherein the filter cake is extruded to form vermicelli or pellets beforethe drying step.
 8. The method of claim 1, wherein the yeast formulationcomprises dry viable yeasts mixed with one or more dry nutrientsselected from inactivated yeasts, yeast autolysates, yeast hulls, yeastextracts, amino acids, peptides, proteins, sterols, ergosterols,thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine,minerals and inorganic nitrogen in the form of ammonium salts.
 9. Themethod of claim 8, wherein the nutrients constitute 10% to 70% by weightof the yeast formulation.
 10. The method of claim 8, further comprisinginactivated yeast mixed with the dry viable yeast.
 11. The method ofclaim 8, wherein the dry viable yeast constitutes at least 20% by weightof the dry weight of the yeast formulation.
 12. The method of claim 11,wherein the dry viable yeast constitutes more than 60% by weight of thedry weight of the yeast formulation.
 13. The method of claim 8, whereinthe yeast formulation is produced by mixing the dry viable yeast and thenutrients in the form of a cream, filtering the cream and thereafterdrying a filter cake.